This invention relates to vapor compression cycle devices of variable capacity and, more particularly, to a means and a method for controlling the capacity modulation of a vapor compression cycle device.
To better accommodate varying heating or cooling demands, a vapor compression cycle device should be provided with a means to vary its capacity. Several methods have been disclosed which enable such a capacity modulation, including the method disclosed in copending patent application Ser. No. 926,510, filed July 20, 1978, now U.S. Pat. No. 4,217,760 and assigned to the assignee hereof. This particular approach utilizes the thermodynamic properties of certain multi-component working fluid mixtures in a two accumulator device to enable the variation of the capacity of that device. The present invention discloses an improved means and method for controlling the capacity modulation of a device of this type.
Capacity modulation in devices such as that disclosed in U.S. Pat. No. 4,217,760 is achieved by exploiting certain thermodynamic equilibrium properties between interfacing liquid and vapor phases of a miscible multi-component working fluid mixture. In particular, advantage is derived from the fact that the density of mixture vapor is a function of the composition of an interfacing mixture liquid. Accordingly, by connecting a compressor suction line of a device with an accumulator in which a charge of mixture liquid is maintained, changes in the composition of the liquid will have a direct affect on the density of the vapor entering the compressor, and thus can directly affect the device capacity. The composition of this liquid is in turn varied by regulating the flow rate of mixture liquid from a high pressure accumulator of the device, which liquid typically has a different composition than does the liquid contained in a low pressure accumulator.
Control of the mixture liquid flow rate from the high pressure accumulator, and thus control over device capacity modulation, has typically been accomplished through the use of an adjustable flow-restricting device located in a flow path intermediate the high and low pressure accumulators. Although this is an effective control system, a simpler, more dependable and less costly control system would be preferable in many applications, such as in refrigerators. Accordingly, the present invention is an improvement over prior variable capacity vapor compression cycle devices of this type in that it provides a simplified, dependable control system.
Additionally, the present invention may beneficially extend the lifetime of compressors which have previously been adversely affected in conventional vapor compression cycle devices by high startup loads following periods of inoperation, such as after defrost cycles in refrigerator applications. The present invention as described hereinbelow achieves a decrease in compressor startup load by storing additional working fluid in a high pressure accumulator of the device prior to shutting off the system compressor. Thus, the compressor is confronted with a decreased load during a subsequent startup, thereby beneficially extending the lifetime of the compressor.
Accordingly, it is an object of the present invention to provide a new and improved vapor compression cycle device.
It is a further object of the present invention to provide a simplified means and method for controlling the capacity modulation of a vapor compression cycle device.
Still another object of the present invention is to extend the lifetime of a vapor compression cycle device compressor through a reduction of compressor startup loads.